It is known to transmit power over data lines to power remote equipment. Power over Ethernet (PoE) is an example of one such system. In PoE, limited power is transmitted to Ethernet-connected equipment (e.g., VoIP telephones, WLAN transmitters, security cameras, etc.) from an Ethernet switch. DC power from the Ethernet switch is transmitted over two sets of twisted pair wires in the standard CAT-5 cabling. The same two sets of twisted pair wires may also conduct differential data signals, since the DC common mode voltage does not affect the data. In this way, the need for providing any external power source for the Powered Devices (PDs) can be eliminated. The standards for PoE are set out in IEEE 802.3, incorporated herein by reference. The CAT-5 cable has four twisted wire pairs, and two of the wire pairs are typically not used.
A more recent development is called Power over Data Lines (PoDL), where only one twisted wire pair carries both differential Ethernet data and DC power. Such a system also uses PSEs and PDs. PoDL is particularly attractive for automobiles due to the minimum wiring needed. Any electronic device may be powered by the PoDL system. The DC voltage transmitted by the twisted wire pair in an automobile will usually be 12 volts. The IEEE has developed the 802.3bu standard for PoDL.
In both PoE and PoDL, there is a low power detection phase that is conducted before the full DC voltage is applied to the wires. The detection phase looks for a signature from the PD that indicates that the PD is compatible for PoE or PoDL. There may also be a low power classification phase following the detection phase, where the power requirements of the PD are conveyed. The PSE then supplies the full DC voltage, by closing a switch coupled between the power source and the wires, after it determines that it can supply the required power. Controller ICs for PoE are commercially available that carry out the various routines, close a switch to apply the full DC voltage to the wires, and detect faults.
Although PoE and PoDL are advantageous for use in an automobile (and other applications) due to the reduced wiring leading from the PSE to each PD, it would be desirable to further reduce the required wiring while improving reliability.